(a) Field of the Invention
The present invention relates to a structure for guiding the installation of a thermowell for temperature sensor and a method for installing a thermowell for temperature sensor by using the structure.
(b) Description of the Related Art
In general, the catalytic gas phase oxidation occurring in a reaction tube is highly exothermic, and it is very important to monitor the temperature of the catalyst bed accurately and control the reaction temperature accordingly. Typical examples of such a manufacturing process include a process for manufacturing acrolein or acrylic acid by oxidizing propylene or propane, a process for manufacturing phthalic anhydride by oxidizing naphthalene or orthoxylene, and a process for manufacturing maleic anhydride by partially oxidizing benzene, butylene, or butadiene.
During such a manufacturing process, the temperature is measured in the axial direction of the reaction tube, and is referred to as an axial temperature profile. When it comes to the temperature profile, the location of hot spots and the temperature size at that location vary depending on the construction and activity of the catalyst bed, the reaction temperature, the reaction pressure, and the flow rate of reaction mixtures. Therefore, it is of crucial importance to measure the temperature inside the catalyst bed accurately.
Based on the measured temperature, any excessive increase of temperature at the hot spots inside the catalyst bed or thermal accumulation near the hot spots must be avoided. This is because the high temperature occurring otherwise degrades the selectivity of the product.
In order to monitor the temperature of hot spots of a fixed-bed catalyst reaction tube and obtain a temperature profile of the entire catalyst bed, a thermowell for temperature sensor is installed, and a thermocouple, for example, is placed inside the thermowell while filling the reaction tube with a catalyst.
When a thermowell for temperature sensor is to be positioned at a desired location on a catalyst bed (e.g. at radial center), it is customary to install fixed supports (e.g. wires) on the thermowell at an interval in the axial direction.
However, if a reaction tube is filled with a catalyst while a thermowell for temperature sensor is positioned in the reaction tube by fixed supports, they interfere with the filling path and result in irregular filling. As a result, the density of the catalyst bed fluctuates. In addition, the coefficient of thermal transfer may vary due to the influence of materials constituting the supports. This adversely affects the temperature measurement.
Particularly, if the porosity of the catalyst bed increases locally, most reaction substances tend to pass through the highly porous portion (i.e. channeling occurs). In the case of a heat exchange-type multi-tubular reactor, an enormous load is concentrated on a fraction of contact tubes among tens of thousands of them. For these reasons, it is of great importance to maintain a uniformly filled bed.
When the catalyst needs replacement when its life has expired or when it has been damaged, the supports installed on the thermowell for temperature sensor make it difficult to remove the catalyst from the contact tubes.
A thermowell for temperature sensor having no support may be used in order to avoid these problems. Although this approach may alleviate the irregularity of filling and the deviation of density of the catalyst bed, it becomes difficult to maintain the thermowell for temperature sensor at a desired location in the radial direction of the catalyst bed. Particularly, the thermowell for temperature sensor tends to bend and adhere to the wall of the reaction tube or deflect in an unwanted direction. As a result, it is not easy to measure the temperature at a desired location.